Thin film transistors (TFTs) have been widely applied in flat-panel display device due to their perfect switching characteristic.
Generally, a TFT comprises a gate, an active layer, a source and a drain. The source and the drain are disposed separately at two ends of the active layer, and are contact with the active layer respectively. When voltage of the gate is higher than threshold voltage of the gate, the source are electrically connected to the drain through the active layer, and carriers flow from the source to the drain or from the drain to the source.
The active layer of TFT is generally formed by using material of metallic nitrogen-oxide, such as zinc gallium oxynitride, zinc indium oxynitride, zinc aluminum oxynitride, zinc oxynitride (ZnON), and the like. When the TFT is in ON state, trap state for transmission of the carriers may be formed by oxygen vacancies in the metallic nitrogen-oxide, which may decrease transmission rate of the carriers and increase subthreshold swing of TFT. The increased subthreshold swing may impact on operation capacity of TFT seriously.
In addition, contact resistances between the active layer and the source, the drain are usually large, which also impacts on the transmission of the carriers, resulting in larger subthreshold swing of TFT, and thereby impacting on operation capacity of TFT seriously.